1. Field of the Invention
The present invention generally relates to a device for simulating a rectified constant impedance load and a method thereof, more particularly to a device that simulates a rectified constant impedance load via an active electrical load.
2. Description of the Prior Art
An AC power product, such as UPS, etc., is widely applied in our normal life. And the scope of such application comprises general information, communication, consumer electronics, transportations, industry, military, etc. The functions to the power products are to drive electrical components and maintain voltages so as to keep a whole system working well. Hence, the main factors to the design of a power device are to decrease cost and increase liability.
General AC power products are mostly for routine works, and sometimes are no-loaded. The load characteristic of the routine work equipment is RLC (resistor, inductor, capacitor) load. Therefore, the characteristics of such AC power products are tested by RLC load. And a designer must consider the application situations of RLC load while in the step of design, that is, the control circuit shall be focused for stability.
General rectified AC load can be simulated by a network consisted of passive components as resistor, inductor, capacitor, diode, etc. And the manufacturers directly use such components to form a load circuit, as shown in FIG. 1A, which illustrates a schematic view of a rectified constant impedance load circuit. The disadvantage of such circuit is the volume thereof will be huge while demanding larger power; and it is inconvenient to adjust resistor value, capacitance value or induction value.
With reference to FIG. 1A, which represents that using a rectified constant impedance load (RECTCZLOAD) to test the characteristics of the AC power product. The rectified constant impedance load 100 includes a bridge rectifier 102, a serial resistor Rs, a serial inductor Ls, a load capacitor C, and a load resistor RL. The bridge rectifier 102 is usually consisted of four diodes in order to adjust the input voltage of an AC power product 200 to be the format of whole wave. The load capacitor C and the load resistor RL are a parallel connection, and then the parallel connection is serially connected to the bridge rectifier 102, the serial resistor Rs and the inductor Ls in order to form a rectified constant impedance load network for testing the AC power product 200. While the AC power product 200 is connected to the network and an output voltage is produced, the output load current is then known; further, the variation of the voltage caused by the load network is known as well.
With reference to FIG. 1B, which illustrates a voltage/current variation chart of testing the rectified constant impedance load of FIG. 1A. The rectified constant impedance load has a characteristic of pull as described below. When the load applied to the DUT, due to the output impedance characteristics (generally inductive), the output voltage of the DUT will be distorted when the load current has a value of higher CF (>2.5), which represent the steepness of the load current. Higher is the CF, larger the distortion of the output voltage of the DUT will be.
As aforesaid, the rectified constant impedance load may need resistors, capacitors, inductors, bridge rectifiers, etc. Each component will also need some other different components. Especially the volumes of the serial resistors Rs and the load resistors RL are huge, thus the idea of using an electrical load means for simulation is then produced.
However, general AC electrical load only provides the functions with certain currents, certain power, etc. Such functions are set by a controller and without the consideration of the voltage variation of the tested object; thus, a designed load waveform is directly drawn. Due to the load control signal without referring to the voltage of the tested object, an instance response can not be made for the output voltage variation of the tested object. So, the real simulation for the load characteristic can not reach.
Therefore, how to figure out the disadvantages of prior arts is an important issue to the skilled people in the art.